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Discrimination and Phylogeny of Solenogaster Species Through the Morphology of Hard Parts (Mollusca, Aplacophora, Neomeniomorpha).

AMELIE H. SCHELTEMA [*]

CHRISTOFFER SCHANDER

Abstract. Ten species in five genera and three families from continental shelf and deep-sea collections of neomenioid Aplacophora (Mollusca) are described, emphasizing external anatomy and hard parts--body shape, radula, epidermal spicules, and copulatory spicules--as well as the reproductive system. One genus and seven species are new: Plawenia n.g., Plawenia sphaera, P. argentinensis, Dorymenia tortilis, Eleutheromenia bassensis, E. mimus, Kruppomenia levis, and K. delta. Also included are redescriptions of three published species, emphasizing hard parts for comparisons with the new species and genus: Dorymenia sarsii (Koren & Danielssen), Simrothiella margaritacea (Koren & Danielssen), and Plawenia schizoradulata (Salvini-Plawen). A cladistic analysis of species described here demonstrates the usefulness of hard parts for phylogeny. Specimens came from collections made in the southwest Pacific and the southwest and northeast Atlantic.

Introduction

Aplacophora are vermiform, spicule-covered molluscs that are most numerous and have the greatest diversity of species at depths greater than 200 m in the sea. But their internal anatomy seems to be primitive for the Mollusca, and the vermiform shape derived, a combination thought to be the result of progenesis (Scheltema, 1993, 1996). Aplacophora comprise two taxa, the Neomeniomorpha (=Solenogastres) and the Chaetodermomorpha (=Caudofoveata). Most neomenioids creep by means of a narrow foot on mud bottoms or on hydroids and octocorals upon which they feed; they are hermaphrodites. Chaetoderms are burrowers, feeding upon foraminifera or organic detritus; they are dioecious.

Of the two Aplacophora taxa, we believe the neomeniolds are the less derived (Scheltema, 1993, 1996; Scheltema et al., 1994; Ivanov, 1996), and are thus particularly important in considerations of the phylogeny of molluscs. However, the opposite view--that they are more derived--has been expressed (Salvini-Plawen, 1985; Salvini-Plawen and Steiner, 1996).

There are at present fewer than 250 described neomenioid species. However, every deep-sea and continental shelf sample taken with modern equipment, and processed by elutriating the collected sediment through fine screens ([less than]0.4 mm mesh size), will contain at least a few, and sometimes more than a dozen, neomenioid species. Moreover, in regions never before sampled, many or most of these species will be new. By our present estimates, which are based both on the number of undescribed species already collected and on the vast areas of the deep-sea benthic fauna that have yet to be sampled, there are probably some 1000 species worldwide.

Although the works of Salvini-Plawen have raised important evolutionary issues (especially 1972, 1985; also, Salvini-Plawen and Steiner, 1996), aplacophorans have not received broad attention, owing in large part to the difficulty of obtaining living specimens (but see Salvini-Plawen, 1968; Morse, 1979; Morse and Norenberg, 1992; Scheltema and Jebb, 1994). Also, we suggest that the inadequate taxonomic characterization, particularly of neomenioids, has prevented most biologists from becoming seriously involved with them. Authors of most monographs of neomenioids have concentrated on internal anatomy as understood from histology (e.g., Nierstrasz, 1902; Heath, 1911, 1918; Odhner, 1921; Salvini-Plawen, 1978). An important consequence of histological preparation is that hard structures are dissolved or destroyed, and have thus been poorly illustrated. Moreover, careful drawings and photographs of entire organisms have seldom been published (but see Scheltema and Kuzirian, 1991). A few isolated epidermal spicule s may have been drawn, but at too small a scale for comparisons with other species. Radulae have not been isolated for illustration; the radular teeth have either been drawn as part of a histological section or reconstructed from sectioned material. Copulatory spicules, which dissolve during histological preparation, have practically never been illustrated at all, yet they are often the most important structures for species determination (e.g., Eleutheromenia species; see below). The absence of hard-part and external morphology from neomenioid descriptions reduces the value of the characterization--like describing the soft anatomy of a gastropod, but not its shell or isolated radula. As deep-sea ecologists collect more neomenioids, they are thus unable to identify them from the literature.

This paper therefore focuses on external anatomy and on the morphology of isolated hard parts. Descriptions of genera and species are arranged as follows: Diagnoses of genera are arranged in the following order: appearance, spicule type, cuticle, epidermis, radula, and particulars of anatomy from anterior to posterior. Species Descriptions are divided into Appearance, Cuticle and epidermis, Epidermal spicules, Radula, Copulatory spicules, Notes on anatomy, and Reproductive system. Following both diagnoses and descriptions are Remarks on particulars for species discrimination, problems of classification, and notable anatomical features or puzzles. We expect that specialists and nonspecialists alike will be able to use these descriptions to identify similar species at least to genus.

A second aim of this paper was to perform a preliminary phylogenetic analysis based on both the hard-part morphologies and the soft anatomy briefly described here (particularly the reproductive system). We hope that, as new deep-sea collections become available, this paper will serve as a useful model for describing neomenioid species and for investigating their phylogenetic relationships.

General Anatomy of Neomeniomorpha

Recent accounts of aplacophoran anatomy are given in Salvini-Plawen (1985) and Scheltema et al. (1994). A generalized illustration of a neomenioid may be found in Figure 1.

The first characteristics one notices in a neomenjoid are the size and shape of the body, and the attitude of the myriad, usually shining aragonite spicules covering the animal--that is, the outer appearance (Fig. 11C, E). Body shape varies from almost spherical (Fig. 19D) to greatly elongate (Fig. 6A), and the length of mature individuals varies from 1 or 2 mm to 10 cm or more (Fig. 11C, F). A neomenioid may be spiny, smooth, or rough (Figs. 6, 11). The shape of retracted mouth and mantle-cavity openings may be diagnostic (Fig. 15C, H).

The cuticle and epidermis can be either thick or thin relative to the size of the species. A thick cuticle can occur with a thin epidermis, or a thin cuticle with a thick epidermis, or they may be the same thickness. Gland cells of the epidermis, termed papillae, may have long stalks or be unstalked (Fig. 1B, EP); their function has not been determined.

The epidermal spicules can be (1) skeletal ( = tangential)--the spicules lie within the cuticle, at right angles to each other, in one or more layers, spiraling from ventroanterior to dorsoposterior and from dorsoanterior to ventroposterior (Fig. 20A); (2) upright (=radial)--arranged in a single layer, more or less erect, usually with the distal ends extending beyond the cuticle (Fig. 19); and (3) adpressed, with a single layer of overlapping spicules lying flat against the body wall cuticle (e.g., Tegulaherpia; see Scheltema, 1999a, fig. 3A). Species may exhibit one arrangement, a combination of (1) and (2) (Fig. 12A, D), or a combination of (2) and (3) (e.g., Acanthomenia; see Scheltema, 1999b, fig. 2). Spicules may be rounded and hollow with a wall surrounding a single space, or solid and flat or rounded, and encompass a variety of shapes and sizes; several types may occur within a single species. The spicules beside the pedal groove are somewhat arcuate, or at least convexly curved on one side, and are a rranged in a single longitudinal row on each side of the pedal groove; they often bear a "handle," or root (Fig. 8B spicule 5, and Fig. 20G). Most neomenioids have a few to numerous specialized spicules at the entrance to the mantle cavity; these are presumably used in copulation (Fig. 4K, L).

The radula of neomenioids may have two teeth per row (distichous) (Figs. 11B, 21A), one tooth per row (monostichous) (e.g., Acanthomenia, see Scheltema, 1999b, fig. 3A, B), or many teeth per row (polystichous) (Fig. 2E, F). The terms "bisenial" and "monoserial" are ambiguous, having been applied to both a divided radular membrane and a radula with two teeth per row (Scheltema, 1981); these terms are not used here. Distichous radulae are of two types: they are formed of (1) bars entirely attached to the radular membrane and bearing denticles or serrations (Figs. 12F, G, 19E, G), or (2) denticulate hooks mostly free of the radular membrane (Fig. 11D). A radula is lacking in 20% of known species. Both distichous and polystichous radulae lack a central, median tooth like the rachidians in gastropod radulae, the only exception being in some species of Proneomeniidae (e.g., Garcia-Alvarez et al., 1998). In distichous radulae, the largest denticles are lateral (Figs. 7H, J, 17A, 21F); during growth, denticles are a dded either medially or by the bifurcation of a pre-existing denticle (Fig. 7H). In many species, the radula passes into, and is enclosed by, an anteroventral radular pocket, or pair of pockets (Figs. 1 AVP; 6B, 19F).

One or more copulatory spicules are found in many species of neomenioids (Fig. 14). They are largely or entirely calcitic (Figs. 4A, 9) and secreted in deep, usually paired pockets of the mantle cavity; they are thus of epidermal origin. Accessory spicules may be present (Figs. 20C, 22B, D). The exact function of copulatory spicules has never been determined. They are deciduous or become resorbed in some species, and some may be one-third the total length of an individual.

Notes on anatomy are given here for various species, according to their importance to that species for discrimination or for defining membership in higher ranks. The tetraneural nervous system, not described here, is morphologically quite constant among neomenioids. Examples may be found in Salvini-Plawen (1985) and Scheltema et al. (1994).

Salivary glands are associated with the radula or, if the radula is absent, with some part of the pharynx (Fig. 1, VSG, SG). In this work, the types of ventral salivary glands were determined according to Welsch and Storch (1973), rather than according to Salvini-Plawen (1978). The glands are usually ventrally paired, simple, multicellular, tubular glands that are elongate or saclike (Figs. 5A, 6B). They are sometimes acinar, or occur in groups of single goblet gland cells, or are compound.

The midgut dominates the midregion of the body and is extensive in elongate species. It is sacculate (i.e., with lateral pouches) in those species where the midgut wall is interrupted by serially repeated, lateroventral muscles (see Scheltema et a!., 1994, fig. 13C). A dorsal cecum may extend anteriorly above the pharynx (Fig. lA, DC; Scheltema et al., fig. 8C).

The mantle cavity contains one or two gametopores, the anus, openings of the copulatory spicule sacs, and usually respiratory folds or papillae. There is usually a dorsoterminal sense organ on the outer dorsal wall of the mantle cavity.

For most species herein, the reproductive system is described. As in the chaetoderms, it is unique among molluscs, because the gonads, with only a single exception, empty through paired gonopericardial ducts directly into the pericardial cavity (Fig. lB, GPC); in other molluscs, the gonads empty through gonoducts that bypass the pericardium. The gametes thus pass through the pericardium before entering the (usually) U-shaped, paired, upper and lower gametoducts (=pericardioducts and spawning ducts or shell glands; Stachowitsch, 1992) (Fig. 1B, GD1, GD2). The lower gametoducts, in turn, empty into the small posterior or posteroventral mantle cavity through paired gametopores; or the lower gametoducts unite before opening through a single gametopore. Usually, one or more paired seminal receptacles are found near the union of the upper and lower gametoducts (Figs. 1B, SR; 5A, 5). Seminal vesicles are uncommon; where they do occur, they are found in conjunction with either the gonopericardial ducts or the upper gametoducts (Fig. 6C). Internal fertilization is inferred from the presence of seminal receptacles, from introsperm morphology (Buckland-Nicks and Scheltema, 1995), and from observation of living Epimenia (Scheltema and Jebb, 1994).

Materials and Methods

Species were selected from the following collections of Aplacophora: West European Basin (INCAL, 15 July to 11 August, 1976, Centre National de Tri d'Oc6anographie Biologique [CENTOB]; and RV Chain Cruise 106, 15 August to 6 September, 1972, Woods Hole Oceanographic Institution); off Gibraltar (BALGIM, 25 May to 22 June, 1984, CENTOB); Bass Strait (Bass Strait Survey 1979-1984, Museum of Victoria, Australia); and Argentine Basin (RV Atlantis II Cruise 60, 10.iii-30.iii.1971).

Taxonomy. Holotypes were drawn under a dissecting microscope equipped with an ocular drawing tube and then photographed. Measurements were made on drawings, either with a map wheel or with dividers. The length of a specimen in lateral view is measured along the axial midline; two diameters, the dorsoventral height and lateral width, are measured in lateral and either dorsal or ventral view, respectively.

Epidermal spicules were dislodged with a needle, either into glycerine in a depression slide or into distilled water on a flat slide; in the latter case, they were then air dried and covered with a coverslip and mountant. These isolated spicules were then illustrated with the aid of an ocular drawing tube. Solid spicules were examined under cross-polarized light, which is broken up into birefringent color bands by the aragonite crystals of the spicules; selected isochromes were drawn and their thickness determined.

Radulae and copulatory spicules were isolated and prepared as follows. The anterior and posterior ends of an individual were cut off and placed in a depression slide with a drop of commercial hypochlorite solution (household bleach), which dissolves the tissue. The radula or copulatory spicules were then teased away from the remaining cuticle and epidermal spicules. The preparations were washed several times by carefully adding and drawing off distilled water with a pipette, and a drop of glycerine was then added. When radular teeth were to be examined with an oil immersion lens, either a temporary or permanent slide was made. In the first case, the radula was transferred into glycerine on a flat slide, and a coverslip was added. To make a permanent slide, the radula was washed in distilled water, then pipetted into a drop of a water-miscible mountant (CMCP-10) on a slide and a coverslip added. After drawings had been made of copulatory spicules in glycerine on a depression slide, permanent slides were prepa red. The spicules were washed with distilled water and transferred to a slide with the aid of a micropipetter, which can pick up and release individual spicules. After air-drying, a mountant and coverslip were added. Measurements of radulae, epidermal spicules, and copulatory spicules were made with an ocular micrometer.

Histologic sections were cut at 7 [micro]m (paraffin embedded) or at 1.5 or 3.0 [micro]m (Epon embedded). The former were stained with hematoxylin and Gray's double contrast or with Mallory-Heidenhain trichrome; the Epon sections were stained with azure II and methylene blue. All drawings of sections have the following conventions: (1) double lines, no stippling, cell walls not indicated: gonopericardial ducts, seminal receptacles, copulatory spicule sacs; (2) single line: dorsal sinus, pericardium, heart; (3) double lines, stippling only: seminal vesicles; (4) double lines, cell walls, no stippling: upper gametoducts, rectum, mantle cavity; (5) double lines, stippling, cell walls: lower gametoducts.

Holotypes, paratypes, and voucher specimens are deposited in, or were borrowed from, the following museums: MNHNP, Musdum National d' Histoire Naturelle, Paris; MV, Museum of Victoria, Melbourne; UIB.Z.M, University of Bergen Zoological Museum, Norway; USNM, National Museum of Natural History, Washington, DC.

Phylogeny. The data matrix for a cladistic analysis was created with MacClade version 3.04 (Maddison and Maddison, 1992). The exhaustive search option in PAUP version 4.0b1 (Swofford, 1998) was used to reconstruct the phylogeny, and MacGlade was used for subsequent analysis and interpretation of trees. Decay values (Bremer, 1988, 1994) were calculated with AutoDecay version 4.0 (Eriksson, 1998), and bootstrap and jacknife values were calculated with PAUP version 4.0b1 with 1000 replicates.

Systematic Account

NEOMENIOMORPHA Pelseneer, 1906

Ventroplicida Boettger, 1956; Solenogastres Gegenbaur, 1878 [partim], Salvini-Plawen, 1967. Non Neomeniamorpha Salvini-Plawen, 1978.

Diagnosis: Aplacophoran molluscs with a narrow foot-fold in a ventral, longitudinal pedal groove and without a cuticular oral shield or mantle cavity ctenidia; midgut as a combined stomach and digestive gland; monoecius.

Remarks: The telltale ventral groove in a spicule-covered, cylindrical organism immediately identifies it as a neomenioid mollusc.

PRONEOMENIIDAE Simroth, 1893

Type genus. Proneomenia Hubrecht, 1880.

With two genera, Proneomenia Hubrecht and Dorymenia Heath.

Dorymenia Heath, 1911

Type species. Dorymenia acuta Heath, 1911, by monotypy [Bull. Zool. Nom. 38:185].

Known distribution. Reported from the northeast, southeast, and southwest Pacific Ocean, northeast and northwest Atlantic Ocean, Mediterranean Sea, off East Indies, and Antarctica; 21 species are described from 50 to 3200 m depth.

Diagnosis. Body elongate, slender, smooth, to 10 cm long, with or without posterior fingerlike projection; skeletal spicules hollow, in several layers; upright spicules, if present, solid, paddle-shaped, small; cuticle thick; epidermis thin, with long, stalked epidermal papillae extending through the cuticle; radula polystichous, largest teeth in each row lateral, tooth rows on each side of median line mirror images, some species with a median tooth; anteroventral radular pocket single (Fig. 6B); ventral salivary glands tubular, long, ducts paired or single; midgut sacculate; with one or more dorsoterminal sense organs; paired seminal receptacles single; gametopore single; with paired copulatory spicules; gill folds greatly reduced; mantle cavity with one or more deep anterior pockets.

Remarks. Proneomenia and Dorymenia may be synonyms. The sole criterion for separating the two genera is the presence (Dorymenia) or absence (Proneomenia) of copulatory spicules (see, e.g., Salvini-Plawen, 1978). Dissolution of copulatory spicules is evident in some individuals of both D. sarsii and D. tortilis, but it is not known whether empty copulatory spicule sacs are retained. However, Hubrecht's (1881) description of the type species Proneomenia sluiteri includes illustrations of paired, ventral mantle cavity pockets that appear to be empty copulatory spicule sacs.

Dorymenia sarsii (Koren & Danielssen, 1877)

(Figs. 2C, E, 3A, B, 4E, G, H, J, L)

Neomenia sarsii Koren and Danielssen, 1877; Proneomenia sarsii (Kor. & Dan.), Hansen, 1889; Simrothiella sarsii (Kor. & Dan.), Pilsbry, 1898; sarsi of authors.

Lectotype (Odhner, 1921 [as "prototype"]). UIB.Z.M 2074 (alcohol specimen, anterior and posterior ends missing, removed before Odhner's [1921] investigations; spicule slide): Length [greater than] 40 mm, height 1.5 and 1.2 mm at anterior end and midbody, respectively. Kristianiafjord [Oslo Fjord], 190-225 m, coil. G. 0. Sars.

Voucher specimens. UIB.Z.M 19850: Length [tilde]32 mm, height 2.0 and 1.5 mm at anterior end and midbody, respectively. Herlofjord, 150 m (alcohol specimen, posterior end dissected; spicule slide). UIB.Z.M 53025: Length 46 mm, height 1.9 and 1.4 mm at anterior end and midbody, respectively. Osefjord, 60[degrees]30'30"N, 6[degrees]55'40"E, 206 m (alcohol specimen, anterior and posterior ends dissected; spicule, radula, and copulatory spicule slides).

Material examined. Lectotype and three lots from the Bergen Museum (UIB.Z.M 53024, 53025, 19850).

Description.

Appearance: With characters of the genus; with posterior fingerlike projection (Fig. 2C). Lengths of examined specimens to 46 mm, height at midbody to 1.5 mm (53 mm by 2.3 mm, Odhner [1921]; 70 mm by 3 mm, Koren & Danielssen [1877; trans. 1879]); anterior height to 2.0 mm; posterior projection to 2.0 mm long, height to 0.5 mm.

Cuticle and epidermis: Cuticle 40 to 50 [micro]m thick, epidermis thinner.

Epidermal spicules: Skeletal spicules to 330 [micro]m long, 19 [micro]m wide, curve shallow, solid distal tips to 25 [micro]m long, wall thickness to 6 [micro]m proximal end straight, to 45 [micro]m long; spicules [less than] 110 [micro]m in length few (Fig. 3A, B). Upright paddle-shaped spicules sparse, to 103 [micro]m long, 11 [micro]m wide, curved, distal end rounded, bases narrow to wide (Fig. 3B, spicules 1, 2). Spicules from beside pedal groove solid, of two types: (1) flat, thin spicules, one margin straight, the other convex, with narrow root, to 120 [micro]m long, 13 [micro]m wide, [less than]3 [micro]m thick (spicule 4); (2) curved spicules lateral to type 1 round in cross-section with narrow base, to 135 [micro]m long, 9 [micro]m wide (spicule 3).

Radula (one examined, numbers in parentheses from Odhner [1921]): With 14 (16) teeth per row, rows about 28 ([greater than]30), with median furrow, length of teeth from 48 [micro]m at median furrow to 93 [micro]m at lateral margin, tooth bases narrow, 10 [micro]m or less (Fig. 2E).

Copulatory spicules (2 individuals examined): Spicules undergoing dissolution in one individual, but accessory copulatory spicules and mantle cavity edge spicules intact; copulatory spicules (Fig. 4E, G) with a short, flaccid hyaline region below a solid, calcium carbonate distal end 500 [micro]m long by 90 [micro]m wide; bent, pointed tip 70 [micro]m long, 20 [micro]m at its widest; calcitic portion medially grooved; accessory copulatory spicules to 315 [micro]m long by 28 [micro]m wide, rounded at both ends, triradiate in cross-section (Fig. 4J); epidermal spicules at opening of mantle cavity truncated distally at an angle, to 95 [micro]m long, 8 [micro]m wide (Fig. 18L); in second individual no copulatory spicules present, accessory copulatory spicules undergoing dissolution (Fig. 4H), and mantle cavity edge spicules not found.

Reproductive system: Not re-examined here.

Remarks. The spelling of this species is sometimes found in the literature as sarsi, an unnecessary emendation of sarsii (for Sarsius: Bull. Zool. Nom. 38:185--186). The exceptional dimensions given by Koren and Danielssen (1877, 1879)), greater than reported or seen since for this species, may be a twofold measuring error; the greatest height of the lectotype is 1.5 mm, reported as 3 mm by Koren and Danielssen. The authors also reversed anterior and posterior ends in their verbal description of body shape. That the lectotype was properly chosen by Odhner (1921) seems to be in no doubt, as it was collected by Sars and is from the type locality.

Dorymenia sarsii appears to be a continental shelf species from Scandinavian waters. The attribution of Dorymenia sp. in Scheltema et al. (1994) to D. sarsii is not correct (Salvini-Plawen, 1997), and does not extend the geographic distribution of D. sarsii to the Iberian shelf region.

Dorymenia tortilis sp. n.

(Figs. 2A, B, F, 3C, 4A--D, F, K, 5, 6A--E)

Dorymenia sp., Scheltema et al., 1994 [not D. sarsii, Salvini-Plawen, 1997, p. 48], figs. 5c, 7b, l0c, llc, 13a, b, d--f, 18c, 22e, 23f, 24e, g.

Holotype. MNHNP (alcohol specimen, spicule slide): Length 36.1 mm, height 1.7 mm at anterior end and mid-body. NW of Gibraltar, 36[degrees]50.4'N, 9[degrees]14.9'W, 681 m, BALGIM [CENTOB] CP-03.

Illustrated paratypes 1, 2. MNHNP (no. 1, dissected alcohol specimen; radula, spicule slides); (no. 2, dissected alcohol specimen; spicule, copulatory spicule slides). Type locality.

Material examined. Eight individuals from type locality.

Description.

Appearance: With the characters of the genus; with a posterior fingerlike projection (Figs. 2A, B, 6D); holotype largest individual examined.

Cuticle and epidermis: Cuticle thick, 116 [micro]m; epidermis thin, 12 to 14 [micro]m, with oval to quadrate papillae borne on long, slender stalks.

Epidermal spicules: Skeletal spicules to 325 [micro]m long, 18 [micro]m wide, curve pronounced, solid tip to 24 [micro]m long, wall thickness to 5 [micro]m, proximal end straight, length to 45 [micro]m; short hollow spicules [less than]110 [micro]m numerous (Fig. 3C). Upright paddle-shaped spicules deeply curved, distally pointed, to 117 [micro]m long, 13 [micro]m wide, base broad (Fig. 3C, spicules 1, 2). Spicules from beside pedal groove solid, of two types: (1) flat spicules, one margin convex, the other concave, to 128 [micro]m long, 13 [micro]m wide, [less than]3 [micro]m thick, with root (spicule 4); (2) lateral to type 1, curved spicules round in cross-section, base narrow to broad, to 153 [micro]m long, 9 [micro]m wide (spicule 3).

Radula (2 examined) with 14 teeth per row, number of rows about 44, length of medial teeth 28 [micro]m lateral teeth 85 [micro]m tooth bases broad, 10 to 15 [micro]m (Fig. 2F).

Copulatory spicules (2 examined): Spicules in one individual undergoing dissolution (Fig. 4D); the other with intact spicules (Fig. 4A, F); intact spicule 2.4 mm long by 60 [micro]m wide, with solid, calcium carbonate distal end and long, stiffened, hyaline region twisted around a stiff, hollow, hyaline rod forming a core (Fig. 4A); twisted region stiffened by densely scattered crystals of calcium carbonate aligned with the turns and at angle to each other, spicule less twisted proximally; solid distal end broadly grooved on opposite sides, 270 [micro]m long, 55 [micro]m greatest width in intact spicule, with a bent, pointed tip 38 [micro]m long, 18 [micro]m wide. An isolated, presumably developing solid end not attached to a proximal hyaline portion, tip 50 [micro]m long, 20 [micro]m wide, and an isolated, hollow hyaline core 1.5 mm long, 21 [micro]m wide, also present in individual with intact spicules (Fig. 4B, C).

Notes on anatomy: Anteroventral radular pocket extending posteriorly beneath radular sac (Fig. 6B), with distal teeth undergoing dissolution (Fig. 6E). Paired salivary glands with united ducts opening into base of pharyax beneath radular sac (Fig. 6D). Radular sac divided proximally (Fig. 6B). Dorsoterminal sense organ single, with a large dorsal blood vessel.

Reproductive system: In common with other Dorymenia species, paired seminal receptacles single, and anterior pockets of mantle cavity deep (Fig. 5A, B, G; see also Salvini-Plawen, 1978). Dorsal, distal ends of upper gametoducts with three pockets appearing to function as seminal vesicles (Fig. 5A C, D, 6C). In common with D. sarsii (Hansen, 1889), a large, distal, ventral lobe present on each lower gametoduct just before paired gametoducts unite (Fig. 5E, F). Gametoduct opening into the mantle cavity single (Fig. 19G). Distal ends of copulatory spicules borne on papillae.

Remarks. Dorymenia tortilis differs from D. sarsii in its (1) broader radular tooth bases, (2) more numerous tooth rows, (3) greater curvature of the skeletal spicules, (4) more numerous short epidermal spicules, (5) greater length and curvature of the paddle-shaped spicules, (6) shape of spicules beside the pedal groove, (7) shorter solid distal ends of the copulatory spicules, (8) spicules at the entrance to the mantle cavity hooked and larger, and (9) absence of accessory copulatory spicules.

Only one other north Atlantic species, D. peroneopsis Heath, has a fingerlike terminal extension of the body (Heath, 1918). The type material is unknown, but two recently collected individuals from the North American Basin probably belong to this species. They differ from both eastern Atlantic species in larger size, broader anterior and posterior ends (Fig. 2D), lack of paddle-shaped upright spicules, and presence of paired, fanlike arrays of either copulatory spicules or accessory spicules seen within the open mantle cavity.

PRUVOTINIDAE Heath, 1911

Pruvotiniidae Heath, 1911. Pararrhopaliidae Salvini-Plawen, 1972.

Type genus. Pruvotina Cockerell, 1903.

Remarks. The taxon is poorly defined. Taxa with a combination of hollow upright barbed epidermal spicules, curved hollow skeletal and upright spicules, and a distichous radula with denticulate hooks include Pruvotina, Pararrhopalia Simroth, 1893, Eleutheromenia Salvini-Plawen, 1967, Labidoherpia Salvini-Plawen, 1978, and Gephyroherpia Salvini-Plawen, 1978; they were divided into two subfamilies on the basis of salivary gland morphology (Salvini-Plawen, 1978). Lophomenia Heath, 1911, Halomenia Heath, 1911, Metamenia Thiele, 1913, Hypomenia van Lummel, 1930, and Forcepimenia Salvini-Plawen, 1969, included in two other pruvotinid subfamilies (Salvini-Plawen, 1978), lack barbed spicules.

Eleutheromenia Salvini-Plawen, 1967

Paramenia Pruvot, 1890 [non Brauer & Bergenstamm, 1889] [partim]; Pruvotina Cockerell, 1903 [partim]; Perimenia Nierstrasz, 1908.

Type species. Paramenia sierra Pruvot, 1890, by monotypy.

Known distribution. Bass Strait and off southeast Australia; western Mediterranean; at depths of 50 to 400 m.

Diagnosis. Small, spiny, stout, with hollow, barbed, upright spicules; with or without dorsal carina; cuticle and epidermis thin, without stalked papillae; radula with distichous hooks; multicellular dorsal salivary glands not opening through a papilla; ventral salivary glands saclike with tubular ducts; midgut not sacculate or indistinctly so; with an elongate pericardial cavity forming an anterior glandular sac ("sac ovigere" of Pruvot [1891]); pericardial glands present; seminal receptacles as saclike extensions of lower gametoducts; with copulatory spicules; mantle cavity with numerous long respiratory papillae; dorsoterminal sense organ present.

Remarks. When new collections of E. sierra from the type locality (Mediterranean) become available, the relationship between E. sierra and the two new species described here can be reevaluated.

Eleutheromenia bassensis sp. n.

(Figs. 7E-H, 8A, 9A-D, 11F)

Holotype. MV F83480 (alcohol specimen, spicule slide): Length 2.3 mm, height 0.6 mm, width of anterior end 0.7 mm. Bass Strait, Australia, 38[degrees]56.0'S, 145[degrees]16.6'E, 70 m (RV Tangaroa Stn BSS-S 55 [epibenthic sled], 12.xi.1981).

Illustrated paratypes. MV F83481 (dissected alcohol specimen; slides of epidermal and copulatory spicules); MV F83482 (dissected alcohol specimen; copulatory spicule slide). Type locality.

Material examined. 52 individuals, Bass Strait Survey November 1981, RV Tangaroa (number in parentheses; BSS-S, epibenthic sled samples; BSS-G, Smith-Maclntyre grab samples): BSS-S 155, 38[degrees]56.0'S, 145[degrees]16.6'E, 70 m (25); BSS-G 155, 38[degrees]55.5'S, 145[degrees]17.0'E, 70 m (1); BSS-S 156, 39[degrees]45.9'S 145[degrees]33.5'E, 74 m (1); BSS-S 157, 40[degrees]10.9'S, 145[degrees]44.3'E, 75 m (1); BSS-S 162, 40[degrees]09.4'S, 147[degrees]32.6'E, 51 m (7); BSS-G 181, 38[degrees]39.8'S 144[degrees]18.2'E, 79 m (2); BSS-S 195, 39[degrees]38.2'S, 143[degrees]07.2'E, 127 m (2);

BSS-G 195, 39[degrees]38.2'S, 143[degrees]07.2'E, 127 m (1); BSS-S 201, 39[degrees]08.3'S, 144[degrees]43.9'E, 66 m (2); BSS-S 202, 39[degrees]00.2'S, 144[degrees]33.9'E, 74 m (8); BSS-S 205, 39[degrees]13.6'S. 143[degrees]55.6'E, 85 m (2).

Description.

Appearance: Very spiny, to 3 mm in length (Figs. 7E, 11F); anterior width to 0.7 mm, height 0.6 mm or less; rounded anteriorly, somewhat truncated posteriorly; retracted mouth opening triangular; pedal pit a lateral slit (Fig. 7F); pedal groove covered by numerous long epidermal spicules; mantle cavity opening subterminal, spicules in brushes on each side, copulatory spicules often protruded (Fig. 7G), dorsoterminal sense organ often externally visible.

Cuticle and epidermis: Cuticle [less than] 25 [micro]m thick, epidermis about 10 [micro]m thick.

Epidermal spicules: Both skeletal and upright spicules numerous, narrow, evenly curved, tapered at both ends, often slightly recurved at base (Fig. 8A); upright spicules to 400 [micro]m long and 9 [micro]m wide, with solid tips usually to 55 [micro]m, a few to [greater than]60 [micro]m (Fig. 8A spicules 3); skeletal spicules less than 200 [micro]m long and to 8 [micro]m wide, hidden externally under thickly set, upright spicules; barbed spicules numerous, upright, in longitudinal bands on each side of mid-dorsal crest of crossed upright spicules, to 145 [micro]m long and 9 [micro]m wide, shortest anteriorly, sharply recurved twice at base (spicule 2); upright spicules from anterior end near mouth senate (spicules 1); spicules along pedal groove to 100 [micro]m in length, with a short, narrow base (spicule 5); spicules from opening of mantle cavity S-shaped and pointed ovals (spicules 4).

Radula (2 specimens examined): With 21 to 22 rows, teeth 40 to 45 [micro]m by 10 [micro]m, with 4 to 6 denticles (Fig. 7H).

Copulatory spicules (7 specimens examined): copulatory spicules paired, 2 per sac; one long, rodlike, distally tapered and curved, to 750 [micro]m long by 25 [micro]m wide; the other nearly as long, the distal half flared into a hood with a thickened distal ridge, width 104 [micro]m (Fig. 9A-D).

Notes on anatomy: Large dorsal sinus present, extending far anteriorly. Midgut cecum paired anteriorly, becoming single at level of radula. Mantle cavity surrounded by subepithelial goblet cells.

Reproductive system. As in E. mimus.

Remarks. Morphological differences between E. bassensis, E. mimus, and E. sierra are discussed under Remarks for E. mimus.

Eleutheromenia mimus sp. n.

(Figs. 7A-D, J, 8B, 9E-G, 10, l1D, E)

Eleutheromenia sp., Scheltema et al., 1994, figs. 3a, c, 7a, 16c, 20a (identification in caption in error), e, 24d.

Holotype. MV F83474 (alcohol specimen, spicule slide): Length 3.1 mm, height 0.8-0.9 mm, width 1.0 nun. Bass Strait, Australia, 38[degrees]52.6'S, 148[degrees]25.2'E, 140 m (RV Tangaroa Stn BSS-S 170 [epibenthic sled], 15.xi.1981).

Illustrated paratypes. MV F83475 (dissected alcohol specimen, epidermal and copulatory spicule slides); MV F83476 (dissected alcohol specimen, epidermal spicule slide, radula slide); MV F83477 (dissected alcohol specimen, copulatory spicule slide). Type locality.

Material examined. 33 individuals (number in parentheses; all samples from epibenthic sled): Bass Strait Survey, November 1981, RV Tangaroa stations BSS-S 169, 38[degrees]57.8'S, 148[degrees]26.5'E, 120 m (3) and BSS-S 170, 38[degrees]52.5'S, 148[degrees]25.2'E, 140 m (20); RV Franklin July 1986, Slope station 40, 38[degrees]17.7'S, 149[degrees]11.3'E, 400 m (10).

Description.

Appearance: Similar to E. bassensis (Figs. 7A--D, 11E); to 4.4 mm long, height and width to 0.9 mm except width to 1.2 mm at anterior end.

Cuticle and epidermis: Cuticle to 23 [micro]m thick, epidermis thinner, to 16 [micro]m thick.

Epidermal spicules: Types and shapes as in E. bassensis (Fig. 8B); upright spicules to nearly 600 [micro]m long and 13 [micro]m wide, solid tips to 55 [micro]m (spicules 3); many skeletal spicules [less than]200 [micro]m long and to 11 [micro]m in width (spicule 6); barbed spicules to 185 [micro]m by 9 [micro]m, shortest anteriorly (spicules 2); spicules from beside pedal groove usually [less than]100 [micro]m by 14 [micro]m (spicule 5); spicules from opening of mantle cavity S-shaped and pointed ovals (spicules 4).

Radula (2 examined): Number of tooth rows 23, teeth 65 [micro]m by 10 [micro]m, denticle number 5 to 9 (Fig. 7J, 11D).

Copulatory spicules (5 specimens examined): Paired, 2 spicules per copulatory spicule sac, rod-shaped spicule to 830 [micro]m by 32 [micro]m, grooved distally, scarcely tapered, not curved distally; hoodlike spicule [greater than]120 [micro]m wide, with heavy distal ridge and portion of hood distal to ridge deeply curved (Fig. 9E-G).

Notes on anatomy: A pedal commissure sac of unknown function present (see Scheltema et al., 1994, fig. 2c).

Reproductive system: With a large, thick-walled, glandular anterior sac of the pericardial cavity beginning as paired lobes on either side of midgut, becoming a single sac further posteriorly (Fig. 10A-F); cells large, vacuolated, with small, deeply staining granules; sac connecting with mantle cavity through a long, tubelike, dorsoanterior extension of mantle cavity, just anterior to beginning of heart and pericardium proper (Fig. 10F, G); tubelike mantle cavity extension passing around rectum. Gonads emptying into pericardium through unusually long, paired gonopericardial ducts that open into posterior, rather than anterior, part of pericardium (Fig. 10E-J). Pericardium proper short relative to anterior glandular sac. Posterior end of pericardial cavity with pericardial glands (Fig. 10H, J). Seminal receptacles as saclike anterior extensions of the lower gametoducts, without distinct ducts, but separated from gametoducts by a short, tubelike constriction (Fig. 10B, line). Lower gametoducts paired until uni ting just as they reach mantle cavity anterior to the tubelike mantle cavity extension that connects with glandular pericardial sac (Fig. 10D). Upper gametoducts arising as usual from ventroposterior end of pericardium and leading forward, joining lower gametoducts just posterior to union of seminal receptacles with lower gametoducts (Fig. 10C-H).

Remarks. E. mimus differs from E. bassensis in its (1) larger size, (2) longer and wider epidermal spicules, (3) longer radular teeth, (4) more denticles per tooth, and (5) copulatory spicule morphology. The morphology of the copulatory spicules differentiates the two species unequivocally. The rod-shaped spicule in E. bassensis is curved distally and is narrower and more tapered than in E. mimus, whereas the hoodlike spicule in E. mimus bears a heavier ridge and is more deeply curved distally than in E. bassensis. It is likely that E. bassensis also has a pedal commissure sac, but this structure was seen only in 1.5-[micro]m sections of E. mimus. Depth ranges of the two species differ but overlap: E. bassensis has been collected from 70 to 127 m, and E. mimus from 120 to 400 m. They did not occur together in samples, however. Both species differ from E. sierra in size and epidermal spicule morphology and lack the distinct dorsal carina of E. sierra. Seminal receptacles were considered to be lacking in E. si erra (Pruvot, 1891).

The function of the large, glandular pericardial sac at the anterior end of the pericardium is not clear. The sac is only indirectly connected with the gonads through the long gonopericardial ducts that enter the pericardial cavity at its posterior end. Other species of Pruvotinidae are known to have brood chambers, but these are extensions of the mantle cavity, not the pericardium (Salvini-Plawen, 1978).

SIMROTHIELLIDAE Salvini-Plawen, 1978

Type genus. Simrothiella Pilsbry, 1898.

Diagnosis. Neomenioids with body shapes from stout to elongate; epidermal spicules solid or hollow, with or without skeletal spicules; radula distichous with many rows, denticles on a barlike base entirely attached to radular membrane; with paired anteroventral radular pockets either long and spiraled, or short, retaining initial teeth in some taxa.

Remarks. The taxon is currently constituted primarily on the basis of radula morphology (Simrothiella Pilsbry, 1898, Cyclomenia Nierstrasz, 1902, Kruppomenia Nierstrasz, 1903, Uncimenia Nierstrasz, 1903 [lacking a radula], Biserramenia Salvini-Plawen, 1967, Birasoherpia Salvini-Plawen, 1978, Sialoherpia Salvini-Plawen, 1978, Helicoradomenia Scheltema & Kuzirian, 1991, and Plawenia n.g., herein). From the diagnosis above, monophyly of the taxon can be seen to be doubtful and is not reflected in the results of the cladistic analysis below.

Kruppomenia Nierstrasz, 1905

Type species. Kruppomenia minima Nierstrasz, 1905, by monotypy.

Simrothiella Pilsbry, 1898 (partim), Salvini-Plawen, 1972.

Known distribution. Norwegian fjords, West European Basin, and the Mediterranean from 100 m or less to [greater then]4000 m.

Diagnosis. Stout, small; epidermal spicules hollow, both skeletal and upright; epidermis and cuticle thick; radula ribbon broad with many distichous tooth rows, teeth as extremely narrow bars bearing numerous tiny denticles; anteroventral radular pocket retaining first-formed, triangular tooth; ventral salivary glands short, tubular, paired; with paired saclike seminal receptacles; copulatory spicules 2 or more per copulatory spicule sac; respiratory mantle-cavity folds present; a dorsoterminal sense organ present.

Remarks. This genus is represented by several undescribed species in the West European Basin and adjacent waters. A second species, besides the type, has previously been described (K borealis Odhner, 1921). Copulatory spicules tend to be numerous and elaborate in this genus and serve to distinguish species.

Kruppomenia levis sp. n.

(Figs. 6F, H, 12A-C, F, G, 13A, 14A-D)

Holotype. MNHNP (alcohol specimen, spicule slide): Length 3.3 mm, heights 0.7, 0.9, and 0.9 mm anteriorly, at midbody, and posteriorly, respectively; widths 0.7, 1.1, and 0.9 mm. Bay of Biscay 47[degrees]29.8'N, 9[degrees]39.2'W, 4327 m (INCAL [CENTOB] OS-08, 11.viii.1976).

Paratypes. No. 1, MNHNP (dissected alcohol specimen, epidermal and copulatory spicule slides), Bay of Biscay 47[degrees]34.8'N, 9[degrees]33.3'W, 4228 m (BIOGAS VI [CENTOB] DS-76, 23.x.74); no. 2, MNHNP (dissected alcohol specimen, copulatory spicule slide), West European Basin 47[degrees]29.8'N, 9[degrees]33.4'W, 4268 m (INCAL [CENTOB] DS-16, 9.viii. 1976); no. 3, MNHNP (dissected alcohol specimen, epidermal spicule slides), type locality.

Material examined. 22 individuals; see Table 1, with two additional stations: BIOGAS VI (CENTOB) DS-76 (4) and BIOGAS VI DS-77, 4240 m, 47[degrees]31.8'N, 9[degrees]34.6'W, 24.x.74 (4).

Description.

Appearance: Small, stout, length to 3.9 mm, height to 1.3 mm, height and width greatest at midbody, rounded at both ends (Figs. 6H, 12A); appearance somewhat spiny when epidermal spicules intact, but usually appearing smooth (levis) to rough owing to broken state of upright spicules and sediment held between spicules; skeletal spicules forming an open meshwork; contracted mouth opening a vertical slit in flat, circular area without spicules (Fig. 12B); with raised ridge on each side of pedal groove; terminal spicules long and brushlike, meeting at angle above mantle cavity opening (Fig. 12C); cuticle easily torn.

Cuticle and epidermis: Cuticle thick, up to 38 [micro]m; epidermis from thin to thick, 13 [micro]m anteriorly to 38 [micro]m posteriorly, with large, juxtaposed papillae.

Epidermal spicules: Asymmetric, fragile, hollow (Fig. 13A), walls about 2 [micro]m, removable from cuticle only with difficulty; skeletal and upright spicules could not be differentiated, probably similar; many spicules long, to 290 [micro]m anteriorly and 365 [micro]m posteriorly; most distinctive spicules (Fig. 13A, spicules 1, 2, 4, 6, 9) curved from distal end to an abrupt bend 25 to 80 [micro]m above base, widest at bend, to 18 [micro]m, solid tips short, most 11 [micro]m long but to 23 [micro]m, often constricted and bent beyond hollow space that fills most of spicule from tip to base; other spicules evenly curved from tip to base (spicule 8), or recurved proximal to bend (spicule 6); spicules from beside pedal groove 1-2 [micro]m thick, base truncated, with distal nipple, to 106 [micro]m long and 23 [micro]m wide, thickest along outside curve and at base (spicules 13, 14); triangular and paddle-shaped, solid, thin (1-2 [micro]m) spicules present posteriorly, to 100 [micro]m and 115 [micro]m long, resp ectively, probably from beside pedal groove near mantle cavity opening (spicules 10-12).

Radula (3 examined): About 185 [micro]m long, with about 88 rows of narrow, distichous bars bearing numerous tiny (2 [micro]m) denticles and a lateral thickening seen only in histologic sections; teeth bending about one-quarter of the distance from lateral margin, making an axial ridge along length of radula (Fig. 12F, G); most recent teeth 2 [micro]m wide and to 74 [micro]m from lateral to medial margin; first-formed tooth triangular (Fig. 6F); radular apparatus with large bolsters, anteroventral radular pocket broad, paired; proximal end of radular sac divided.

Copulatory spicules (3 individuals examined): 4 per pocket (Fig. 14A-D, spicules 1-4): spicule 1 hollow, elongate, length to [greater than]575 [micro]m, distally pointed, basally tapered, curved, twisted around long axis and appearing either proximally broad and distally narrow or proximally narrow and distally broad (cf. spicules 1, Fig. 30A, B), distal points of paired number 1 spicules held in close proximity in situ; spicules 2 and 3 hollow, distally hooked, narrow, widest just below hook, greatest lengths [greater than]412 [micro]m and 273 [micro]m, respectively; spicule 4 shortest, proximally broad and partially wrapped around spicule 1, recurved twice and axially twisted, to 260 [micro]m long; a fifth, very short (46 [micro]m) hook in one of paired groups (Fig. 14A) may be new spicule in formation.

Notes on anatomy: Pedal pit large, not obvious externally in contracted state. Anterior pharynx a long, narrow tube; midgut not sacculate, with single dorsal cecum. Dorsoterminal sense organ present, not obvious. Mantle cavity with about 46 elongate, slender respiratory papillae.

Reproductive system (not illustrated): Paired seminal vesicles present at posterior ends of gonopericardial ducts. Paired, elongate seminal receptacles empty through long ducts into the unpaired lower gametoduct, which empties dorsally into mantle cavity. Pericardial cavity extending as a narrow, inverted U, both laterally and posteriorly, far over the mantle cavity. Paired upper gametoducts leave the lateral, posterior ends of the pericardial cavity as narrow tubes; anteriorly their relationship to seminal receptacles and lower gametoduct was unclear in examined specimen.

Remarks. Some individuals of Kruppomenia levis have numerous epidermal spicules with constricted tips (Fig. 13A, spicules 4, 9), whereas in others they are scarce. For differences between K. levis and K. delta, see remarks under K. delta.

Kruppomenia delta sp. n.

(Figs. 6G, 12D, E, H-K, 13B, 14E-J)

Holotype. MNHNP (alcohol specimen, spicule slide): Length 2.7 mm, heights 0.6, 0.9, and 0.7 mm anteriorly, at midbody, and posteriorly, respectively, widths 0.9, 0.9, and 0.8 mm. Bay of Biscay 47[degrees]27.3'N, 9[degrees]36.2'W, 4307 m (INCAL [CENTOB] OS-06, 9.viii.1976).

Illustrated paratypes. No. 1, MNHNP (dissected alcohol specimen, epidermal spicule slide); no. 2, MNHNP (dissected alcohol specimen, epidermal spicule slide); type locality. No. 3, MNHNP (dissected alcohol specimen, copulatory spicule slide); Bay of Biscay 47[degrees]29.8'N, 9[degrees]39.2'W, 4327 m (INCAL [CENTOB] OS-08, ll.viii.1976).

Material examined. 10 individuals; see Table 1.

Description.

Appearance: Small, stout, similar to Kruppomenia levis, but smaller; largest individual 2.8 mm, greatest height 0.9 mm, greatest width 0.9 mm; rounded at both ends (Figs. 6G, 12D); appearance somewhat spiny when epidermal spicules intact, but upright spicules often broken, with sediment lodged between them; skeletal spicules forming loose meshwork, cuticle easily torn; contracted mouth triangular in flat, circular area (Fig. 12E); with raised ridge on each side of pedal groove; terminal spicules just above mantle cavity opening long and brushlike, forming tuft (Fig. 12D); otherwise, posterior spicules shorter than in K. levis.

Cuticle and epidermis: Not examined.

Epidermal spicules: Asymmetric, fragile, hollow (Fig. 13B), walls about 2 [micro]m; removable from cuticle with difficulty; longest spicules [greater than] 225 [micro]m; greatest width to 14 [micro]m (Fig. 13B, spicule 8), but most commonly 7 [micro]m; greatest distance from bend to base 56 [micro]m, most [less than]50 [micro]m (spicules 2, 6, 7, 9); solid tips slender, curved, sometimes with slight distal bend, from 9 to 45 [micro]m long, many[greater than] 20 [micro]m (spicules 1, 4, 6); some spicules evenly curved from base to tip, or straight (spicules 4, 5); spicules from beside pedal groove with tapered base, outer margin flattened, to 101 [micro]m long by 20 [micro]m wide (spicules 11, 12), paddle-shaped spicules not observed, but posterior triangular, solid spicules large (spicule 10), to [greater than] 135 [micro]m long.

Radula (3 examined): Length to 230 [micro]m long, similar to that in K. levis but larger (Fig. 12H), teeth to about 78 [micro]m by 4 [micro]m with a lateral denticle larger than remaining little denticles (Fig. 12K); first-formed tooth triangular (Fig. 12J).

Copulatory spicules (3 individuals examined): Paired, two per sac, one spicule elongate, hollow, to 845 [micro]m long, slender (about 22 [micro]m wide), distal tip straight, solid tip to 255 [micro]m long above hollow space (Fig. 14F, J); second spicule proximal, not seen in its entirety, wrapped part way around elongate spicule (Fig. 14G); distal ends of elongate spicules in close proximity in situ (Fig. 14J). With paired groups of seven accessory copulatory spicules (Fig. 14E, H) held tightly together in order of length, from [greater than]200 [micro]m (range 205-211 [micro]m) to about 100 [micro]m (range 90-110 [micro]m); spicules hollow, but smaller ones nearly solid; both ends curved, meeting medially at bulge with sharp bend, with none to several little bumps at one end below slight hook, fewest bumps on largest spicules; relationship to elongate copulatory spicules not determined.

Notes on anatomy: Neither pedal pit nor dorsoterminal sense organ obvious externally.

Reproductive system: Not examined.

Remarks. Copulatory spicules unequivocally differentiate K. delta and K levis (Fig. 14). Further differences are: epidermal spicules of K delta are (1) more slender and more deeply curved, (2) the largest spicules are shorter, (3) the solid tips are longer and without a constriction, and (4) the distance from the base to the bend is less. (5) Spicules from beside the pedal groove in K. delta are basally tapered and the outside margin bent; in K. levis, the base is truncated and the outside margin smoothly curved. (6) Terminal spicules, if still present after processing through sieves, are long and brushlike over entire posterior end in K. levis, but form a tuft over the mantle cavity opening in K delta. (7) The radula of K delta is larger than in K. levis, and the teeth bear a lateral denticle distinctly larger than the comblike dentides. Both species differ from K. minima and K. borealis by their occurrence at abyssal depths greater than 4000 m, and by body shape from K. minima. Unfortunately the types for K borealis (Zoological Museum, University of Oslo, D 25654 and D 28676) are small, poorly dissected specimens without spicules.

Plawenia gen. nov.

Type species. Simrothiella schizoradulata Salvini-Plawen, 1978.

Known distribution. West European Basin and Bay of Biscay; Argentine Basin; off South Shetland Islands; off Peru; off San Diego, California (undescribed species); Japan Trench. (undescribed species); and off La Redunion Island, Indian Ocean (undescribed species); from 2000 to nearly 6000 m.

Diagnosis. Body rotund, small, spiny; with thickset, hollow, upright epidermal spicules, skeletal spicules lacking; cuticle and epidermis thick; radular teeth with a strong, lateral buttress beneath large, lateral denticles; long, spiral anteroventral radular pockets retaining initial, triangular teeth; with two pairs of pharyngeal salivary glands, the dorsalmost acinar; seminal receptacles paired, bibbed; lower gametoducts first uniting and then becoming bibbed before emptying into mantle cavity through a papilla; copulatory spicules single, paired; a dorsoterminal sense organ present.

Description.

The following applies to all three species herein described: Epidermal spicules long, thin-walled (2 [micro]m or less), gently curved or straight above an often bent and recurved base (Fig. 16); hollow internal space running from close to base nearly to tip in] most spicules; proximal ends fiat in widest spicules, flat to rounded in narrower spicules.

Paired anteroventral radular pockets remarkable, with numerous contained rows of teeth spiraled into fiat, plate-like structures positioned perpendicular to dorsoventral axis of the body; left pocket spiraled counterclockwise, right one clockwise in ventral view (Fig. 19E, F). Teeth with distinctive parts (Fig. 17C, D): (1) a bar thickened laterally into a thick buttress; (2) a serrated or scalloped distal margin of the denticle-bearing membrane; (3) a pair of large, lateral denticles flanking two smaller ones above the buttress; and (4) a medial and distal hemispherical extension of the bar. Original, triangular tooth retained in anteroventral radular pocket (Fig. 17H-K).

Copulatory spicules long, with four distinct sections: (1) a terminal, thickened, conical, curved tip (Fig. 18A-C, F, H); (2) a long, distal, thin-walled, twisted hemispherical channel (Fig. 18F, H) followed by (3) a short, narrow, solid, twisted and furrowed section (Fig. 18E, G, H); and (4) a broad, hollow basal portion (Fig. 18D, E, G). Paired bundles of curved, hollow, thick-walled, accessory copulatory spicules bearing distal protuberances (Fig. 18J, K) present amongst thickly set epidermal spicules adjacent to mantle-cavity opening.

Remarks. No entire, fully developed copulatory spicule was recovered from 10 dissected Plawenia individuals. In two small individuals (1.5 mm in P. sphaera, 1.4 mm in P. argentinensis) the spicules were composed only of distal sections 1 and 2 from just above the solid, yet-to-be-formed midsection (Fig. 1 8F). In five of six larger individuals, the distal sections of the spicules were missing and the spicules broken, either through the solid midsection (Fig. 18D, G), or somewhat above it (Fig. 18E). In one individual of intermediate size, the basal section was beginning to form while the tip was retained (Fig. 18H). Such a constancy between body size and absence of the distal section perhaps indicates that the distal end is deciduous rather than missing as an artifact of dissection.

The biogeographic questions raised by the distributions of the three Plawenia species herein described are provocative. P. schizoradulata lives at 4758 m on the Pacific side of the great eastward-bending parabolic arc that stretches from the southern tip of South America through the Scotia Ridge to the islands lying northeast of the Antarctic Peninsula; the benthos is therefore part of the Pacific fauna. The species is also represented by a single individual from the Atacama Trench off Peru at 5821 in (Salvini-Plawen, 1978; specimen not examined by authors). The Scotia Ridge effectively cuts off the deep stenobathyal bottom fauna of the Pacific from the Atlantic. That P. argentinensis from the Atlantic Argentine Basin at [greater than]4000 m depth shows morphological differences from P. schizoradulata is therefore not surprising; what is puzzling is the close similarity between P. schizoradulata and P. sphaera from only 2091 m in the West European Basin in the northeast Atlantic.

Plawenia schizoradulata (Salvini-Plawen, 1978) (Figs. 15A-C, 16 spicules 1, 4-7, 17A, B, H, 18C, 19A, B) Simrothiella schizoradulata Salvini-Plawen, 1978.

Lectotype (herein designated). USNM 749767 (alcohol specimen, spicule slide): Length 2.6 mm, midbody height and width 1.6 and 1.4 mm, respectively (specimen compressed). Drake Passage off South Shetland Islands, 61[degrees]45'S, 61[degrees]14'W, 4758 in (USARP 4-127, 1.viii.62).

Paralectotypes. USNM 880322 (dissected alcohol specimen, spicule, radula slides): Length 1.1 mm, width and height 0.6 and 0.8 mm, respectively (specimen compressed), type locality. USNM 880323 (alcohol specimen): Length 1.3 mm, width and height both 0.9 mm, type locality.

Description.

Appearance: Small, rotund, length to 3.5 mm, diameter to 1.6 mm, posterior body narrower than anterior end; contracted mouth long, oval, on a broad, circular, flattened anteroventral area; pedal groove nearly hidden by spicules (Figs. 15A-C, 19A).

Cuticle and epidermis: Cuticle thick, 70-80 [micro]m, epidermis thinner, 25 [micro]m (Salvini-Plawen, 1978).

Epidermal spicules of lectotype and paralectotype: Almost all broken (Fig. 16, spicules 4-7; measurements, Table 2); many bent about one-quarter distance or less from base (spicules 6, 7); widest just above bend, base narrowest just below bend, then widening proximally; spicules beside pedal groove pointed distally, base rounded, without root (spicule 1).

Radula (one examined, small 1.1-mm paralectotype): Rows about 25 between proximal end of radular sac and pharynx, and 35-40 within anteroventral radular pockets; pockets with 2.5 whorls (3.5 whorls, Salvini-Plawen [1978], probably from a larger individual) (Fig. 19B; measurements, Table 2); morphology of distal extension of denticle-bearing membrane not determined (Fig. 17A, B); number of denticles on lateral buttress 4.

Copulatory spicules (one examined): Distal tip dissected from small paralectotype, broadly conical, curved, and furrowed, 20 [micro]m wide at distance of 45 [micro]m proximal to tip (Fig. 18); remainder of spicule either not recovered or not yet formed; accessory copulatory spicules, if present, overlooked.

Notes on anatomy: The internal anatomy of P. schizoradulata has been published (Salvini-Plawen, 1978).

Reproductive system: See Salvini-Plawen (1978).

Remarks: For differences from other species, see Remarks under P. sphaera and P. argentinensis and Table 2.

Plawenia sphaera sp. n.

(Figs. 15D, E, 16 spicules 2, 8-11, 17C, D, J, 18B, G, H, K, 19D-G)

Scheltema et al., 1994, fig. 18e.

Holotype. MNHNP (alcohol specimen, spicule slide): Length 2.4 mm, greatest height and width 1.7 and 1.9 mm, respectively. West European Basin, 57[degrees]59.7'N, 10[degrees]39.8'W, 2091 m (INCAL [CENTOB] DS-O1, 15.vii.1976).

Illustrated paratypes. No. 1, MNHNP (epidennal, copulatory spicule slides; radula slide) and no. 2, MNHNP (epidermal, copulatory spicule slides); type locality. No. 3, MNHNP (epidermal, copulatory spicule slides; radula slide) and no. 4, MNHNP (dissected alcohol specimen, copulatory spicule slide), West European Basin, 57[degrees]58.8'N, 10[degrees]48.5'W, 2081 m (INCAL [CENTOB] DS-02, 16.vii.76).

Material examined. 68 individuals. See Table 1, also the following: Bay of Biscay, RV Sarsia (National Institute of Oceanography, Plymouth, UK): stn 44, 43[degrees]40.8'N, 3[degrees]35.2'W, 1739 m, 16.vii.67 (20 individuals), and stn 50, 43[degrees]46.7'N, 3[degrees]38'W, 2379 m, 18.vii.67 (1 individual).

Description.

Appearance: Small, rotund, similar in external appearance to P. schizoradulata but smaller; greatest length, height, and width, 2.9, 1.8, and 1.9 mm, respectively (Figs. 15D, 19D); with slight taper posteriorly; with a cleft in long posterior spicules indicating position of dorsoterminal sense organ (Fig. 15E).

Cuticle and epidermis: Cuticle thick, 45 to 50 [micro]m, epidermis thin, 11 to 12 [micro]m.

Epidermal spicules: Long, slender to broad, thin-walled (Fig. 16, spicules 8-11), shape as in P. schizoradulata but largest spicules longer (Table 2); spicules beside pedal groove with a sharp, distal point and proximally narrowed to a slight stem (spicule 2).

Radulae (7 examined, 4 by light microscopy, 3 by SEM, in individuals ranging in length from 1.5 to 2.7 mm; Figs. 17C, D, J; 19E-G; measurements, Table 2): Number of denticles on lateral buttress 4. Tooth structures locking both adjacent and opposed teeth closely to each other, with tips of denticles proximally overlying serrated, distal membrane of next adjacent tooth (Figs. 17D, 2; 19G), and hemispherical medial margin of bar finely denticulate (Fig. 17D, 4), holding opposed teeth in zipperlike arrangement (Fig. 19E).

Copulatory spicules (examined from 6 individuals 1.5 to 2.5 mm long, Fig. 18B, G, H, K; Table 2): Paired, single spicules, proximal two-thirds of spicule hollow, with wall thickened in two longitudinal bands; distal tip narrow, curved, bluntly pointed; accessory copulatory spicules S-shaped with up to 7 distal protuberances, with hollow extending from base up to 4th protuberance; number of accessory spicules per bundle not determined.

Remarks. Histologic descriptions of P. schizoradulata (Salvini-Plawen, 1978) are also descriptive of P. sphaera, with the additional observation that the more dorsal of the paired pharyngeal glands are acinar. The differences between P. sphaera and P. schizoradulata are as follows: In P. sphaera (1) small individuals are more nearly spherical than small P. schizoradulata, with length:height ratios of 1.0 and 1.4, respectively, in individuals less than 1.6 mm long; (2) many epidermal spicules are longer and broader than most of those in P. schizoradulata; (3) the distal tips of the copulatory spicules are narrower and more pointed; (4) there are fewer denticles per tooth; (5) there are more rows of teeth; (6) the initial radular teeth are shorter; and (7) the cuticle and epidermis are about one-half the thickness of those in P. schizoradulata. Finally, although the differences enumerated here and in Table 2 may seem minor, P. schizoradulata belongs to the abyssal Pacific fauna and P. sphaera to the upper slope fauna of the northeastern Atlantic. That they could be the same species is not likely given their morphological and biogeographic differences.

Plawenia argentinensis sp. n.

(Figs. 15F-H, 16 spicules 3, 12-14, 17E-G, K, 18A, D-F, J, 19C)

Holotype. USNM 880318 (alcohol specimen, spicule slide): Length 3.4 mm, midbody height and width 1.4 and 1.5 mm, respectively. Argentine Basin, 38[degrees]16.9'S, 51[degrees]56.1'W, 4382 m (RV Atlantis II Cruise 60, Stn 242, 13.iii.1971).

Illustrated paratypes. USNM 880319 and USNM 880320 (both as dissected alcohol specimens, epidermal and copulatory spicule slides, and radula slide); USNM 880321 (dissected alcohol specimen, copulatory spicule slide); type locality.

Material examined. 23 individuals from type locality.

Description.

Appearance: Largest, most elongate and least spiny Plawenia species herein described, length to 5.0 mm, height to 1.8 mm, width to 1.6 mm (Figs. 15F, G, 19C); tapered anteriorly, mouth usually protruded with pair of lateral protuberances, contracted vestibule opening often distinct above mouth (Fig. 15H); line of pedal groove distinct.

Cuticle and epidermis: Not examined.

Epidermal spicules: Similar to other two species, but longer and broader (Fig. 16, spicules 12-14; Table 2); spicules from beside pedal groove elongate, distally pointed, without or with slight root (spicule 3).

Radula (2 examined): Teeth without distinct denticles except for the three most recently formed (Fig. 17E, F; measurements, Table 2), otherwise denticles appearing only as rows of slight protuberances; distal margin of denticle-bearing membrane scalloped except medially angular (Fig. 17F).

Copulatory spicules (3 examined): As in P. sphaera, but longer and wider, and solid tip longer (Fig. 18A, D-F; Table 2); accessory copulatory spicules about 19 per bundle, short, narrow, curved but not S-shaped, nearly solid or with hollow in central portion of spicule only, protuberances 1 to 3 (Fig. 18J; Table 2).

Remarks. P. argentinensis differs more from the other two Plawenia species than they do from each other in (1) size and shape of body, (2) erectness and size of epidermal spicules, (3) morphology of radula, (4) size of copulatory spicules, and (5) size and morphology of accessory copulatory spicules.

Simrothiella Pilsbry, 1898

Type species. Solenopus margaritaceus Koren & Danielssen, 1877, by subsequent designation [1981 Bull. Zool. Nom. 38, Op. 1185].

Known distribution. Between about 70 and 2000 m depth off Ireland and in Norwegian fjords.

Diagnosis. Elongate, smooth; epidermal spicules skeletal, hollow, uprights either not obvious or lacking; cuticle thick, epidermis thin with stalked papillae (Odhner, 1921); radula large, with long anteroventral pockets parallel to long axis of body, spiral restricted to proximal end. Monotypic, but with a second undescribed species from the West European Basin.

Remarks. The type species is described here on the basis of external morphology and, for the first time, on hard parts isolated from specimens recently collected in the West European Basin and from a museum specimen collected near the type locality. The internal anatomy was described by Odhner (1921).

Simrothiella margaritacea (Koren & Danielssen, 1877)

(Figs. 1lA-C, 20-22)

Lectotype. UIB.Z.M 2075. Two incomplete specimens are labeled as G.O. Sars material from the type locality, Kvitingsog [Norway], 75-115 m (as Hvidingsoerne, Stavanger, 40-60 fm [=72-108 m] in Koren & Danielssen (1877 [trans. 1879]) and appear to be syntypes; Odhner (1921) called these specimens "prototype." Chosen here as lectotype is the more complete specimen with the anterior end intact; the second specimen is a paralectotype, UIB.Z.M 66806. Other G.O. Sars specimens from 75-95 m off Kopervik near the type locality are not considered syntypes (UIB.Z.M. 2078).

Illustrated voucher specimen. UIB.Z.M 66807: Length 9.5 mm, heights at anterior, midbody, just anterior to the posterior bulge, and posterior, 0.8, 1.0, 0.8, and 0.8 mm, respectively. Kopervik near type locality, 75-95 m.

Illustrated voucher specimens. USNM 894261 (entire alcohol specimen), length 9.5 mm, heights of anterior, midbody, anterior to posterior bulge, and posterior, 0.6, 0.8, 0.5, and 0.7 mm, respectively; USNM 894262 (dissected alcohol specimen, copulatory spicule slide); USNM 894263 (dissected alcohol specimen, radula slide); USNM 894264 (dissected alcohol specimen, radula slide, copulatory spicule slide); USNM 894265 (dissected alcohol specimen, radula slide, copulatory and epidermal spicule slides); USNM 894266 (dissected alcohol specimen); West European Basin, 50[degrees]58.7'N, 13[degrees]01.6'W, 2173 m (RV Chain 106, Stn 316, 18.viii.72).

Material examined. 38 individuals: type material (2); UIB.Z.M. 2078(6), Kopervik, 75-95 m; UIB.Z.M 15852, 62[degrees]01'N, 0[degrees]08'E, [tilde]1400 m (Armauer Hansen Stn 3, 10--l1.v.1914)(4); RV Chain 106 Stn 316, 2173 m (26). Description.

Appearance: Slender, length to 12.0 mm, rounded posteriorly and somewhat pointed subterminally at anterior end (Figs. 20A, B, 1lA, C); greatest diameter anterior, to 1.1 mm in height, narrowing to 0.8 mm or less just before the posterior end which swells to 0.9 mm; greatly contracted individuals with constant diameter (cf Figs. 11C, 20A); immature individuals without posterior swelling; contracted mouth a vertical slit, pedal pit small; contracted mantle cavity opening an anterior-posterior slit commencing on a ventral bulge (Fig. 20A); dorsoterminal sense organ present, not obvious; skeletal spicules obvious as an open meshwork, upright spicules not obvious.

Cuticle and epidermis: Not examined.

Skeletal spicules: Hollow, heavy-walled, to 280 [micro]m long by 18 [micro]m wide, walls 5 [micro]m thick (Fig. 20D); lectotype spicules eroded. [greater than]144 by 16 [micro]m, walls 5 [micro]m (Fig. 20J);

Kopervik voucher, spicules eroded, 170 by 16 [micro]m, walls 5 [micro]m (Fig. 20H); spicules evenly curved and widest above proximal straight or recurved basal section; base up to 67 [micro]m long, solid distal tips to 27 [micro]m long, proximal end rounded; skeletal spicules somewhat shorter anteriorly and posteriorly, to 225 [micro]m; upright spicules small, to 95 [micro]m long by 7 [micro]m wide, curved or bent, hollow space narrow, distal end solid and rounded (Fig. 20E); spicules along pedal groove solid, flat, thin (2 [micro]m), with proximal narrow root, distally pointed, length to 74 [micro]m, greatest width to 14 [micro]m (Fig. 20G); spicules just lateral to these shaped much like skeletal spicules in outline but nearly solid, sharply pointed distally, and shorter, to 106 [micro]m long by 7 [micro]m wide, proximal straight portion to 14 [micro]m long (Fig. 20F).

Radula (6 examined: 1 from Kopervik voucher; 5 from Chain 106 Stn 316): Up to nearly 2 mm long, turning 180[degrees] so that short radular sac and long anteroventral radular pocket parallel each other and long axis of body, with 3 discrete sections (Figs. 11B, 21A, B): section 1, proximal anteroventral radular pocket as 0.2-mm loops, one lying over the other, initial teeth nondenticulate bars 20 by 3 [micro]m (Fig. 21E); next teeth comblike bars about 45 by 9 [micro]m at center of section 1, denticle number 14-18 (Fig. 21D); section 2, main part of anteroventral radular pocket and longest section of radula, about 1 mm long, proximal teeth with bar 50 by 15 [micro]m bearing 17 comblike denticles and a lateral denticle 27 [micro]m long, laterally buttressed (Fig. 21C); teeth of section 2 gradually enlarging anteriorly, largest tooth with bar 130 by 90 [micro]m, lateral denticle to 280 [micro]m long, heavily buttressed, other denticles of bar scattered, small, and varying in pattern and number among individuals (Fig. 21F, G); section 3, radular sac 0.5 to 0.6 mm long with 7-9 developing teeth, long lateral denticles ill-defined, with proximal stretch of membrane 0.2 mm long without defined teeth (Figs. 11B, 21A); at ventral bend of radula from the sac into the pharynx, lateral teeth obvious, pointing anteriorly (Figs. 11B, 21A).

Copulatory spicules (5 examined): Paired, 2 per sac (Fig. 22C); one spicule long, curved, hollow, to 1.2 mm long, 93 [micro]m wide in curved view (Fig. 22G), narrower in view where spicule appears straight (Fig. 22C); solid distal ends pointed and approximated in situ (Fig. 20C), with thick core surrounded by added thin layer of calcium carbonate, perhaps as "wings" (Fig. 22E); second spicule shorter, hollow, to 370 [micro]m long, S-shaped, base partially wrapped around long spicule, from 90 [micro]m in widest view to 30 [micro]m in narrowest, axially twisted such that solid distal end widest in narrowest view of base and narrowest in widest view of base (Fig. 22C, G); single, short accessory spicules paired, to 152 [micro]m, base straight, slightly hollowed proximally, distally solid, deeply curved into distal hook (Fig. 22B, D); growth stages of copulatory spicules (Fig. 22A, B, D, E) imperfectly correlated with size of individual.

Reproductive system: See Odhner (1921).

Remarks. The recently collected material from the West European Basin was identified as Simrothiella margaritacea by comparing the following: (1) epidermal spicule width and wall width with the lectotype and Kopervik voucher spicules (Fig. 20D, H, J); (2) width and shape of the anterior end of the body with the lectotype (Fig. 11A); (3) shape and size of the anterior and posterior ends of the body with the Kopervik voucher; (4) radula with the radula of the Kopervik voucher; and (5) size and shape of copulatory spicules with those from the Kopervik voucher (Fig. 22H).

Elements of copulatory spicules of S. margaritacea are much like those in Kruppomenia levis (cf Fig. 14A). The comblike denticles of early teeth are similar to those in Kruppomenia and Plawenia radulae, but the original tooth in S. margaritacea is a nondenticulate bar, not a triangle.

The radular teeth have not achieved full size when they are first released from the radular sac into the pharynx (Figs. 11B, 21A). Additional growth must therefore take place at the distal end of the anteroventral pocket.

Results of Cladistic Analysis

A single species in each of the 5 genera described here, plus a species with a monostichous radula, Lyratoherpia incali Scheltema (1999b), were the subjects of a cladistic analysis. Twenty-six characters from an original set of 42 were selected for the analysis. The 16 excluded characters were uninformative in the present data set and included such autapomorphies as polystichous and monostichous radulae (Dorymenia and Lyratoherpia, respectively). Of the selected characters, 6 are associated with the radula, 5 with spicules, 11 with soft-part anatomy, and 4 with body shape. The characters and their states are listed in Appendix 1. All characters were treated as unordered and were equally weighted. Since the homology of a number of characters is unknown or disputable, we chose to use presence-absence coding. This type of coding is simple and intuitive, and it has the added advantage that exact homologies between character states need not be known (Pleijel, 1995).

The resulting phylogenetic trees were rooted by outgroup analysis (e.g., Nixon and Carpenter, 1993), with Helicoradomenia juani Scheltema & Kuzirian as the outgroup, since it possesses characters that are considered to be less derived. Among these characters are the radula, which is similar to the radula of the Middle Cambrian Wiwaxia (see Schander and Scheltema, in press), and spicules that are solid, a condition known through ontogeny to be plesiomorphic to hollow spicules (Scheltema and Jebb, 1994).

The cladistic analysis resulted in one shortest tree, 46 steps long (Fig. 23). The overall consistency and retention indices (CI, RI) are 0.5652 and 0.5349, respectively. One dade has a decay index of 4, and the others of 1. The character transformations are found in Appendix 2.

Discussion

The external and hard-part morphologies of the 10 species and 5 genera of neomenioid aplacophorans described here provide a basis for aplacophoran taxonomy (i.e., discrimination of taxa), as well as for phylogeny (i.e., the evolutionary relationships among taxa).

Taxonomy

We conclude that histologic preparations by themselves will not provide morphological evidence adequate for discriminating with certainty among closely related species. For example, the two species of Eleutheromenia are indistinguishable from their soft anatomy, yet hard parts, particularly the copulatory spicules (Fig. 9), do distinguish them, and the differences in size of their epidermal spicules and radular teeth are species related, and not due simply to variation within a species. Only measurements of the largest epidermal spicules were useful for species recognition. Analysis of a large number of spicules from a single individual would be meaningless in this regard, for it would hide the truly distinctive character--the size of the largest epidermal spicules produced in each species.

The two closely related Kruppomenia species are distinguished here on hard parts alone, that is, the differences in radula and copulatory spicule morphology (Figs. 12F--K, 14). Even though the differences in epidermal spicules are subtle, one can, with practice, quickly discern the differing lengths between the base and proximal bend (Fig. 13). Although K. levis and K. delta co-occur in some epibenthic sled samples (Table 1), they should not necessarily be considered sympatric; sled trawls, particularly those taken at abyssal depths, often traverse a mile or so of ocean floor and probably collect organisms from several populations.

Dorymenia sarsii and D. tortilis can be differentiated by the spicules at the opening of the mantle cavity (Fig. 4K, L), as well as by the differences listed under Remarks for D. tortilis. Finally, species of Plawenia are differentiated by a combination of hard-part and external morphologies (Table 2).

Higher taxa can also be determined from hard parts and body shape. Thus, although members of both genera are elongate and smooth, Dorymenia and Simrothiella species have very different radulae (Figs. 2E, F, 21). Plawenia species are immediately recognizable by their nearly spherical bodies with long, hollow spicules that are upright, but not skeletal (Fig. 15, 19A, C, D). Kruppomenia species are brought together by their distinctive, long, broad, ribbonlike radula bearing narrow, serrated teeth, as well as by their short, blunt bodies (Fig. 12). Eleutheromenia species belong to a taxon with hollow, barbed spicules and a radula with distichous hooks.

Soft internal anatomy will always be important for phylogeny and often for the determination of higher ranks. What is emphasized here is that identification of species should not depend on histology, and higher taxa should reflect external and hard-part morphologies.

Phylogeny

Because the bootstrap values were relatively low, and few genera and species were included, we refrain from defining clade names (de Queiroz and Gauthier, 1990; Schander and Thollesson, 1995; Cantino et al., 1997), Although the figured tree (Fig. 23) cannot define clades, the usefulness of characters from hard parts in phylogenetic analyses is clear from the average consistency indexes: for radula characters, 0.58; for soft-part anatomy, 0.59; for spicule characters, 0.47; and for external appearance, 1.

In a reanalysis of 22 published phylogenetic studies of Gastropoda, three types of characters were compared: shell, soft anatomy, and "other," which included the radula (Schander and Sundberg, 1997). The results showed that all three character groups had about the same consistency and retention indices, and the conclusion was that all three types of characters are necessary for proper assessment of evolutionary relationships. We likewise find that all types of characters should be used for aplacophorans.

Although the small data set included here is too incomplete to shed light on evolutionary relationships among all neomenioids, it serves as an example of usefulness of hard parts in cladistic analysis. In particular, there is no support for a clade Simrothiellidae (cf Salvini-Plawen, 1978). The indices do give strong support for the clade Lyratoherpia + Dorymenia, but in the present analysis this clade is based mostly on absences (Appendix 2, node 4 [right arrow] node 5), several arising from derivations of the radular apparatus (Scheltema, Kerth, and Kuzirian, unpubl.). Thus, these two taxa share a condition of being derived, and the cladogram should not be interpreted as indicating monophyly. Future phylogenetic analyses utilizing many more taxa are certain to suggest a different relationship.

Acknowledgments

Specimens were generously provided to us by the Centre National de Tri d'Oceanographie through M. Segonzac; by Howard L. Sanders and J. Frederick Grassle from cruises of the Woods Hole Oceanographic Institution under several grants from the National Science Foundation; and from the Museum of Victoria, Australia. The loan of type specimens from the following Museums is gratefully acknowledged: University of Bergen Zoological Museum; Zoological Museum, University of Oslo; and the U.S. National Museum of Natural History. We wish to thank Thomas Dahlgren, the Tuesday afternoon invertebrate discussion group, and two anonymous reviewers for helpful comments that led us to revise the discussion substantially and to add a preliminary phylogenetic analysis of the neomenioid aplacophorans described here. The following figures, with changes herein, first appeared in the Microscopic Anatomy of Invertebrates, Vol. 5: Mollusca I, pp. 13-54, Wiley-Liss, Inc.: 1A, 4A, 5A, 6C, 9D, and 19E. This work was completed with suppor t from a National Science Foundation PEET grant (Partnerships for Enhancing Expertise in Taxonomy) DEB-9521930 to AHS and from the Radman Ernst Colliander Foundation, Helge Ax:son-Johnson Foundation, Goteborgs Kungliga Vetenskaps- och Vitterhetssamhalle, and Adelbertska Foundation to CS.

Contribution no. 9746 from the Woods Hole Oceanographic Institution.

(*.) To whom correspondence should be addressed. E-mail: ascheltema@whoi.edu

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Swofford, D. L. 1998. Phylogenetic Analysis Using Parsimony. Version 4.0bl. Sinauer Associates, Sunderland, MA.

Welsch, U., and V. Storch. 1973. Comparative Animal Cytology and Histology. Seattle, University of Washington Press.
              Material examined, Kruppomenia levis, K. delta,
                   and Plawenia sphaera (INCAL [CENTOB])
Sample Depth (m)      Lat N            Long W         Date    K. levis
DS-01    2091    57[degrees]59.7' 10[degrees]39.8' 15.vii.76
DS-02    2081    57[degrees]58.8' 10[degrees]48.5' 16.vii.76
CP-0l    2068    57[degrees]57.7' 10[degrees]55.0' 16.vii.76
CP-02    2091    57[degrees]58.4' 10[degrees]42.8' 16.vii.76
DS-05    2503    56[degrees]28.1' 11[degrees]11.1' 18.vii.76
DS-14    4254    47[degrees]32.6'  9[degrees]35.7' 7.viii.76     1
DS-15    4211    47[degrees]33.4'  9[degrees]39.1' 8.viii.76
DS-16    4268    47[degrees]29.8'  9[degrees]33.4' 9.viii.76     3
OS-06    4316    47[degrees]27.3'  9[degrees]36.2' 9.viii.76
OS-07    4249    47[degrees]31.8'  9[degrees]34.3' 10.viii.76    7
OS-08    4327    47[degrees]29.8'  9[degrees]39.2' 11.viii.76    3 [*]
Sample K. delta P. sphaera
DS-01             16 [*]
DS-02             26
CP-0l              3
CP-02              1
DS-05              1
DS-14
DS-15     1
DS-16     1
OS-06     6 [*]
OS-07
OS-08     2
(*.)Type locality.
                  Comparison of three species of Plawenia
                              P.
                        Schizoradulata
Body dimensions
  Maximum length        3.5 mm [1]
  Maximum height        1.6 mm [1]
  Length:height (range) 1.4-2.2
  Length:height (mean)  1.7
Epidermal spicules
  Maximum length,
    midbody             [greater than]458 [micro]m
  Maximum length,
    posterior           --
  Maximum width         21 [micro]m
  Length of solid tip,
    most spicules       [less than or equal to] 18 [micro]m
  Pedal groove, max. 1  90 X 13
    X w X thickness     X 2-3 [micro]m
Radula [2]
  Number of rows        [tilde]65
  Number of whorls      3.5 [1]
  Tooth bar             60 X 10 [mocro]m
  Number of denticles
    above bar           19
  Buttress              19 X 13 [micro]m
  Number of denticles
    above buttress      4
  Length initial tooth  18 [micro]m
Copulatory spicules
  Length of base        n.d.
  Maximum width of
    base                n.d.
  Length solid
    midsection          n.d.
  Length distal section n.d.
  Maximum width
    distal section      n.d.
  Total length [4]      n.d.
  Length conical tip
    above channel       n.d.
  Maximum width
    conical tip         20 [micro]m
  Max. 1. accessory
    copulatory spic.    n.d.
  No. protuberances
    accessory cop.
    spic.               n.d.
                          P.
                        Sphaera
Body dimensions
  Maximum length        2.9 mm
  Maximum height        1.8 mm
  Length:height (range) 1.0-2.2
  Length:height (mean)  1.6
Epidermal spicules
  Maximum length,
    midbody             [greater than]528 [micro]m
  Maximum length,
    posterior           [greater than]700 [micro]m
  Maximum width         20 [micro]m
  Length of solid tip,
    most spicules       [less than or equal to] 18 [micro]m
  Pedal groove, max. 1  86 X 14
    X w X thickness       X 4 [micro]m
Radula [2]
  Number of rows        95-145
  Number of whorls      2.5-3.5
  Tooth bar             74 X 10 [micro]m
  Number of denticles
    above bar           11-15
  Buttress              27 X 17 [micro]m
  Number of denticles
    above buttress      4
  Length initial tooth  14 [micro]m
Copulatory spicules
  Length of base        890 [micro]m
  Maximum width of
    base                60 [micro]m
  Length solid
    midsection          180 [micro]m
  Length distal section 520 [micro]m
  Maximum width
    distal section      30 [micro]m
  Total length [4]      1,590 [micro]m
  Length conical tip
    above channel       36 [micro]m
  Maximum width
    conical tip         17 [micro]m
  Max. 1. accessory
    copulatory spic.    234 [micro]m
  No. protuberances
    accessory cop.
    spic.               7
                             P.
                        argentinensis
Body dimensions
  Maximum length        5.0 mm
  Maximum height        1.8 mm
  Length:height (range) 1.8-3.1
  Length:height (mean)  2.3
Epidermal spicules
  Maximum length,
    midbody             [greater than]725 [micro]m
  Maximum length,
    posterior           [greater than]766 [micro]m
  Maximum width         23 [micro]m
  Length of solid tip,
    most spicules       [less than or equal to] 22 [micro]m
  Pedal groove, max. 1  108 X 15
    X w X thickness       X 3.5 [micro]m
Radula [2]
  Number of rows        146
  Number of whorls      2.8
  Tooth bar             86 X 13 [micro]m
  Number of denticles
    above bar           11-13 [3]
  Buttress              35 X 20 [micro]m
  Number of denticles
    above buttress      4 [3]
  Length initial tooth  18 [micro]m
Copulatory spicules
  Length of base        1,000 [micro]m
  Maximum width of
    base                80 [micro]m
  Length solid
    midsection          180 [micro]m
  Length distal section 678 [micro]m
  Maximum width
    distal section      35 [micro]m
  Total length [4]      1,858 [micro]m
  Length conical tip
    above channel       50 [micro]m
  Maximum width
    conical tip         20 [micro]m
  Max. 1. accessory
    copulatory spic.    196 [micro]m
  No. protuberances
    accessory cop.
    spic.               3
(1.)Salvini-Plawen (1978).
(2.)Radula measurements in P. schizoradulata from small paralectotype
1.1 mm long.
(3.)Present only in firts three most recently formed teeth.
(4.)Estimated total length before presumed loss of deciduous distal
section.
                                Appendix 1
                   Data matrix and list of characters
                          1111111112222222
Taxon/node                12345678901234567890123456
Dorymenia tortilis        00000101?01011110010101101
Eleutheromenia mimus      10000?01?10101011110010010
Helicoradomenia juani     11000010010100101110010110
Kruppomenia levis         11111010110101010010110010
Plawenia sphaera          11101010110100011001001110
Simrothiella margaritacea 11111010001011011001?01101
Lyratoherpia incali       00000100?01010100101100110
(0 .)absent
(1.)present


1. Distichous radula: with 2 teeth per row (Figs. 1lB, D, 12F, H, 19B, E, F, 21)

2. Bar base: radula on a bar entirely attached to radular ribbon (Figs. 6F, 12G, K, 19G, 21)

3. Original tooth: retained in anteroventral radular pocket (Figs. 6F, 12J, 21E)

4. Serrate teeth: denticles as fine serrations (Figs. 6F, 12F, G, H, K, 21D)

5. Tooth buttress: thickened radula base beneath lateral denticles (Figs. 17, 21G)

6. Unipartite membrane: radular membrane not divided (Scheltema, 1988)

7. Paired anteroventral pocket (Fig. 19F, 21A)

8. Single anteroventral pocket (Fig. 6B)

9. Original tooth triangular (Fig. 6F)

10. Stout body shape (Figs. 6G, H, 1lE, F, 19A, C, D)

11. Elongate body shape (Figs. 6A, 1IC)

12. Rounded body ends (Figs. 7A, E, 12A, D, 15)

13. Pointed or lobate body ends (Figs. 2A-D, 11C)

14. Skeletal spicules: spicules within cuticle, at right angles to each other (Figs. 2A, 12A, D, 20A)

15. Solid spicules (Fig. 3 spicules 1-3)

16. Hollow spicules (Figs. 3 [except spicules 1-4], 8, 13, 16, 20D-J)

17. Accessory copulatory spicules (Figs. 18J, K, 20C, 22B and D small spicules)

18. Copulatory spicule hood: main spicule with a second spicule wrapped around it (Fig. 9)

19. Single seminal receptacle (Figs. 5A, 10A, B)

20. Multiple seminal receptacles (Scheltema et al., 1994, fig. 24h, i)

21. Seminal vesicle (Fig. 6C)

22. Respiratory papillae (Scheltema er at., 1994, fig. 1ld)

23. Respiratory folds (Scheltema et at., 1994, fig. 1lc)

24. Midgut sacculations (Scheltema et al., 1994, fig. 13c)

25. Single-cell epidermal glands (Scheltema et al., 1994, fig. 5d-g)

26. Multiple cell epidermal glands (Scheltema et al., 1994, fig. 5a, c)
                     List of character transformations
Branch                       Character
node 1 [right arrow] node 2   3 (Original tooth)
                              5 (Tooth buttress)
                              9 (Triangular original tooth)
                             18 (Copulatory spicule hood)
                             21 (Seminal vesicle)
node 2 [right arrow] node 3  19 (Single seminal receptacle)
                             20 (Multiple seminal receptacles)
                             22 (Respiratory papillae)
                             23 (Respiratory folds)
                             24 (Midgut sacculations)
node 3 [right arrow]  node 4  9 (Triangular original tooth)
                             10 (Stout body shape index [less than] 5
                             11 (Elongate body shape index [greather than
                             or equal to] 5)
                             12 (Rounded body ends)
                             13 (Pointed or lobate body ends)
                             25 (Single-cell epidermal glands)
                             26 (Multiple-cell epidermal glands)
node 4 [right arrow]  node 5  1 (Distichous radula)
                              2 (Bar base)
                              3 (Original tooth)
                              5 (Tooth buttress)
                              6 (Unipartite membrane)
                              7 (Paired anteroventral pocket)
                             15 (Solid spicules)
                             17 (Accessory copulatory spicules)
Branch                       Change
node 1 [right arrow] node 2  0 [right arrow] 1
                             0 [right arrow] 1
                             0 [right arrow] 1
                             1 [right arrow] 0
                             0 [right arrow] 1
node 2 [right arrow] node 3  1 [right arrow] 0
                             0 [right arrow] 1
                             1 [right arrow] 0
                             0 [right arrow] 1
                             0 [right arrow] 1
node 3 [right arrow]  node 4 1 [right arrow] 0
                             1 [right arrow] 0
                             0 [right arrow] 1
                             1 [right arrow] 0
                             0 [right arrow] 1
                             1 [right arrow] 0
                             0 [right arrow] 1
node 4 [right arrow]  node 5 1 [right arrow] 0
                             1 [right arrow] 0
                             1 [right arrow] 0
                             1 [right arrow] 0
                             0 [right arrow] 1
                             1 [right arrow] 0
                             0 [right arrow] 1
                             1 [right arrow] 0
Branch                               Character
node 5 [right arrow] Dorymenia       8 (Single anteroventral pocket)
                                     19 (Single seminal receptacle)
                                     20 (Multiple seminal receptacles)
node 5 [right arrow] Lyratoherpia    14 (Skeletal spicules)
                                     16 (Hollow spicules)
                                     18 (Copulatory spicule hood)
                                     23 (Respiratory folds)
                                     25 (Single-cell epidermal glands)
                                     26 (Multiple-cell epidermal glands)
node 4 [right arrow] Simrothiella    4 (Serrate teeth)
node 3 [right arrow] Plawenia        14 (Skeletal spicules)
                                     21 (Seminal vesicle)
node 2 [right arrow] Kruppomenia     4 (Serrate teeth)
                                     17 (Accessory copulatory spicules)
node 1 [right arrow] Eleutheromenia  2 (Bar base)
                                     7 (Paired anteroventral pocket)
                                     8 (Single anteroventral pocket)
node 1 [right arrow] Helicoradomenia 14 (Skeletal spicules)
                                     15 (Solid spicules)
                                     16 (Hollow spicules)
                                     24 (Midgut sacculations)
Branch                                    Change
node 5 [right arrow] Dorymenia       0 [right arrow] 1
                                     0 [right arrow] 1
                                     1 [right arrow] 0
node 5 [right arrow] Lyratoherpia    1 [right arrow] 0
                                     1 [right arrow] 0
                                     0 [right arrow] 1
                                     1 [right arrow] 0
                                     0 [right arrow] 1
                                     1 [right arrow] 0
node 4 [right arrow] Simrothiella    0 [right arrow] 1
node 3 [right arrow] Plawenia        1 [right arrow] 0
                                     1 [right arrow] 0
node 2 [right arrow] Kruppomenia     0 [right arrow] 1
                                     1 [right arrow] 0
node 1 [right arrow] Eleutheromenia  1 [right arrow] 0
                                     1 [right arrow] 0
                                     0 [right arrow] 1
node 1 [right arrow] Helicoradomenia 1 [right arrow] 0
                                     0 [right arrow] 1
                                     1 [right arrow] 0
                                     0 [right arrow] 1
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Author:SCHELTEMA, AMELIE H.; SCHANDER, CHRISTOFFER
Publication:The Biological Bulletin
Date:Feb 1, 2000
Words:15096
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